1. Field of the Invention
The present invention relates to an optical element, an optical element, a display device, and a three-dimension image display device, and more particularly, to a technique employed by a projection display device, especially, a projection display device using a digital micro-mirror device (abbreviated to be “DMD”) for increasing the resolution of the projection display device.
2. Description of the Related Art
In a so-called “pixel shift technique”, a pixel shift element is used to display image patterns, with display positions of them being shifted by using an optical deflection element in response to deflection of the light path in each sub-field, and thereby, the number of pixels of image display units appears to be doubled. The pixel shift element includes plural image display units arranged two-dimensionally and being controllable according to image information, a light source that emits light to illuminate the image display units, an optical device for observing the image patterns displayed on the image display units, and the aforesaid optical deflection element that deflects the light path from the image display units to optical elements in each sub field. Here, the sub fields are divisions of an image field in time order.
In the following descriptions, by “polarization direction of linear-polarized light”, it means an oscillation direction of the electric filed vector of the linear-polarized light.
In the pixel shift technique of the related art, the image display units or the optical elements of a projecting optical system are allowed to oscillate, alternatively, liquid crystal optical deflection elements are utilized. In the pixel shift technique, which involves oscillation of the image display units or the optical elements, because mechanical oscillation occurs at the same time, durability of the image display units or the optical elements is degraded, and heat or noise is generated. In contrast, the pixel shift technique employing liquid crystal optical deflection elements is superior in mechanical reliability, but if liquid crystal alignment is not sufficient, the contrast of images can be degraded, and due to this, cost of each display element may increase.
Meanwhile, development is being made of a projection display device using a DMD. The projection display device using a DMD includes a device that enables color image display by means of field sequential coloring with a color wheel. Below, detailed descriptions are made with reference to drawings.
FIG. 34 is a diagram illustrating a configuration of a projection display device in the related art.
As illustrated in FIG. 34, the projection display device includes a lamp unit 1, a color wheel 2, a lens 3, a rod integrator 4, a condenser lens 5, a DMD 6, and a projection lens 7.
The lamp unit 1 includes a white light source, such as a high-pressure mercury lamp, or a xenon lamp.
FIG. 35 is a diagram illustrating the composition of the light beam emitted from the lamp unit 1.
As illustrated in FIG. 35, the light beam from the lamp unit 1 has red, blue, and green compositions.
When the light beam from the lamp unit 1 passes through the color wheel 2, the light beam is decomposed into a red light beam, a blue light beam, and a green light beam sequentially. The light beam from the color wheel 2 passes through the lens 3, and is directed to the rod integrator 4, which adjusts the intensity uniformity of the light beam. The light beam passes through the condenser lens 5 and is directed to the DMD 6. The DMD 6 is an image display unit in which micro-mirrors, which serve as pixels, are arranged two-dimensionally. According to the image signal corresponding to each pixel, the orientation (such as angle) of each corresponding micro-mirror is adjusted so as to adjust the time length of reflecting the light beam to the projection lens 7, and the time length of reflecting the light beam to other directions to obtain desired brightness at each pixel.
For example, Japanese Laid-Open Patent
Application No. 2004-070365 (hereinafter, referred to as “reference 1”) discloses a technique, which is similar to the pixel shift technique, for high resolution and smooth images with the DMD by allowing the DMD or the optical elements of the projecting optical system to oscillate.
Japanese Patent Gazette No. 3352100 (hereinafter, referred to as “reference 2”) proposes to use a rotating prism in a display device, in which the rotating prism is used to shift plural color light bands (light stripes from an illumination system) in an image display unit to improve light utilization efficiency when a single-plate display unit is used to display color images.
Japanese Laid-Open Patent Application No. 8-068963 (hereinafter, referred to as “reference 3”) and Japanese Laid-Open Patent Application No. 9-159971 (hereinafter, referred to as “reference 4”) disclose a technique related to a three-dimension image display system. In the three-dimension image display system proposed in the reference 3, a polarized light beam splitter is used to split the light beam from a light source into an S polarized-light component and a P polarized-light component, and the S and P polarized-light components are incident on liquid crystal panels for the right eye and left eye of a viewer, respectively, and are projected on a screen.
In the three-dimension image display system proposed in the reference 4, a polarization adjusting element is provided in front of a lenticular screen to change the polarization direction in time order, and a polarization plate series, which includes polarization filters perpendicular to each other and arranged like a stripe, is used as the lenticular screen.
However, because mechanical oscillation occurs in the display device proposed in the reference 1, durability of the image display units or the optical elements is degraded, and heat or noise is generated.
The display device proposed in the reference 2 is effective for display color images, but it cannot change the polarization direction, hence, it cannot increase the resolution of the DMD.
In the display device proposed in the reference 3, because two groups of image display units and projection lenses have to be prepared corresponding to the right eye and the left eye, the size of the display device is large.
In the display device proposed in the reference 4, because the light beam has to pass through the polarization adjusting element, the quality of image is degraded; in addition, because the light intensity is largely reduced in the polarization plate series, the light utilization efficiency is low.